The union vote-rigging scandal in Falkirk deepened yesterday after a couple living in the constituency disclosed that a “phantom” Labour Party member was signed up at their address.

The couple said they were “mystified” after receiving mail from both the Labour Party and the Unite union for a man they have never met. They have even been visited by individuals looking for the man.

The man is one of 15 Labour Party members identified by Eric Joyce, the MP for Falkirk, who do not live at their registered addresses.

The “phantom” members were signed up during a recruitment drive by Unite, which swelled the party’s membership by more than 100 in just a few months.

The latest disclosure will increase pressure on Ed Miliband, the Labour leader, to reopen his party’s inquiry into the scandal, in which Unite has been accused of conspiring to rig the Labour party candidate selection for Falkirk.

The couple, who asked not to be named, said they began receiving letters for the man more than a year ago. The Daily Telegraph understands that he is registered as a Labour Party member at their address.

The husband said: “Someone from the constituency Labour party turned up at our door around nine months to a year ago looking for him, so they genuinely believe he exists.

“I’m a Unite member but not a Labour member — I just don’t have any interest in any of it. Hopefully someone will get the letters to stop coming.”

The husband works at the Ineos petrochemical plant in Grangemouth, which almost closed with the loss of 800 jobs after the Unite union rejected a survival plan. The plant was saved after the union reversed its decision.

Mr Joyce, who is standing down at the next election, said: “All sorts of murky things have been going on. Ed Miliband needs to take condemn it, he needs to have an inquiring mind and show moral courage.”

A Labour Party spokesman said: “We have taken swift and thorough measures throughout this to uphold the integrity of the Labour Party. We have put the constituency into special measures, we have frozen the local membership which means no member who has joined since Eric Joyce resigned can take part in the selection of a new candidate.”

A Unite spokesman said: “As Mr Joyce and others know full well, Unite has been found by the Labour Party and Police Scotland to have broken no rule or law.”